Static bed agglomeration

ABSTRACT

A method for agglomerating particles of pulverulent food material wherein a static bed of particles is subjected to a hot humid atmosphere sufficient to fuse the static bed into a compacted fused sheet. The fused sheet may be ground to produce strong hard agglomerates of any desired particle size.

United States Patent Meyer et a1.

[ NOV. 13, 11973 STATIC BED AGGLOMERATION Inventors: William J. Meyer,Orangeburg;

Boleslaw Sienkiewicz, Pearl River; John J. Byrwa, Yonkers, all of N.Y.

General Foods Corporation, White Plains, N.Y.

Filed: Oct. 4, 1971 Appl. No.: 186,561

Assignee:

US. Cl 426/453, 99/DIG. 4, 23/313, Int. Cl. A23f l/04 Field of Search99/D1G. 4, 71

References Cited UNITED STATES PATENTS 10/1971 Sienkiewicz 99/D1G. 4

3,433,644 3/1969 Ganske et al. 99/D1G. 4 3,506,457 4/1970 Gidlow et al.99/DIG. 4 3,306,958 2/1967 Gidlow 99/D1G. 4 3,527,647 9/1970 Hager99/D1G. 4

Primary Examiner-Frank W Lutter Assistant ExaminerWilliam L. MentlikAttorney-Thomas R. Savoie et a1.

5 Claims, No Drawings STATIC BED AGGLOMERATION BACKGROUND OF THEINVENTION In many agglomeration processes the particles to beagglomerated are caused to become sticky or tacky and then caused tocontact one another. Various means of tackifying and contacting theparticles to be agglomerated are known in the art.

A common technique of agglomeration involves spraying a stream offalling particles with steam, water or a mixture of steam and air.Agglomeration occurs after or while the particles are passing throughthe spray due to the numerous collisions of the moist sticky particles.After the agglomerates are formed they are usually dried and cooled inan air stream. Such a technique is described in U.S. Pat. No. 3,143,428to Riemers et al. and U.S. Pat. No. 3,527,647 to Hager.

Another agglomeration technique involves the use of hot humidified airflows to at least partially fluidize a moving bed of particles. Theparticles are tackified by means of the hot humid air, and collisionscaused by the fluidization produce agglomerates. The agglomerates arethen dried and cooled usually by means of sep arate air streams. Such aprocess is described in U.S. Pat. No. 3,306,958 to Gidlow, U.S. Pat. No.3,433,644 to Ganske et al. and U.S. Pat. No. 3,471,603 to Patrick et al.

The prior art processes generally require rather large equipment inorder to handle the large air flows inherently used in the processes,and these processes yield a significant amount of fine or unagglomeratedmaterial. Very often the material to be agglomerated must be pretreatedbefore it can be agglomerated by falling through a wet spray;pretreatment may include grinding and/or chilling of the particles.Techniques which involve the use of fluidized beds present the problemof recovering particles entrained in the air flows.

SUMMARY OF THE INVENTION It has now been discovered that particles ofpulverulent food material, even those materials which possess arelatively low moisture content of from 1% to 5%, may be agglomerated,without the addition of large amounts of moisture, by means of a staticbed. According to this invention a static bed of particles is subjectedto a hot humid atmosphere which causes the bed to fuse into a rigidsheet of material. This rigid sheet may then be ground to desiredparticle sizes.

Agglomeration may be caused to take place with the addition of not morethan 1.5% by weight of water to the particles. This enables the processof this invention to proceed with a minimum of drying. Additionally,since the moisture addition is so low and no fluidization is necessaryto promote agglomeration, both agglomeration and drying may take placein the same compartment.

The process of this invention may be conducted as either a batch orcontinuous process. A typical continuous process could convey the staticbed through a fusion zone on a continuous conveyor such as a nonporousmetal belt or a metal screen.

DETAILED DESCRIPTION OF THE INVENTION The process of this invention isparticularly adapted for the agglomeration of materials which tend tohave plastic properties when exposed to a hot humid atmosphere, suchthat particles in contact with each other will be able to fuse together.As used in this invention, fusion is synonymous with melting, welding orcoalescing of the particles at the various contact points of theseparticles when the surface temperature is raised above its thermoplasticpoint.

Inherent in this process is the fact that when the static bed ofparticles is caused to agglomerate by fusion the bed will compact toproduce a relatively dense, hard sheet of material; however, conditionsare controlled so that the sheet will maintain a porous character andnot melt into a solid slab. The fused sheet may be subsequently groundinto various sized agglomerates, each agglomerate being strong and hardand containing a plurality of fused particles.

It is desirable, but not necessary, to adjust the depth of the staticbed such that one dimension of the final agglomerates will be fixed.Normally the beds will be spread to a depth of less than 1 inch. Thiswill enable the fused sheet to be readily ground in conventional millingequipment. Additionally, the use of thin beds will enable a shortresidence time within the agglomeration zone. When employing acontinuous process it will not be practical to work with static beds inexcess of about 0.75 inches.

The process of this invention is particularly useful for agglomeratingsoluble coffee since it has been found that conventional spray driedcoffee powder may be formed into hard agglomerates which resemble chunkyfreeze dried coffee. Other suitable pulverulent materials or mixtures ofmaterials such as sugars and powdered beverage mixes may also be readilyagglomerated in accordance with this invention.

The pulverulent starting material can comprise either free-flowingpowder or granular material and is typically in the range of 20 to 350microns. Preferably the particles should not be so small that they forma tightlypacked, non-porous static bed.

The pulverulent material is initially deposited as a bed upon a support.The supporting member may be either a porous or non-porous surface andmay be either of finite (e.g. tray) or infinite (e.g. continuous belt)length. The supporting member is then either placed into or passedthrough a treatment zone wherein a hot humid atmosphere contacts thestatic bed. The conditioning atmosphere can comprise a mixture of watervapor and hot air, or other heated gases with condensible liquids mayalso be employed.

Agglomeration of the static bed into a fused sheet may take place with aminimum of water being taken on by the pulverulent material. Typicallyless than 1.5% by weight of moisture is added to the pulverulentmaterial in the agglomerating zone. Since the water addition is low aminimum of drying is required and it is therefore possible to bothagglomerate and dry in a single compartment by virtue of a differentialin conditions within the compartment.

The conditioning atmosphere is preferably circulated throughout thetreatment compartment. Care must be taken, however, to maintain thevelocity of the atmosphere at a low speed, usually less than feet perminute, so that the pulverulent material is not disturbed from itsstatic position. When using a porous surface, preferably the atmosphereis caused to pass down through the static bed which may be supported ona porous member. However, upward flow, or even lateral flow ofconditioning atmosphere may be permitted so long as the static particlesare not agitated.

When this invention is employed to agglomerate pulverulent coffeematerial with a low moisture content of less than 5% by weight, asteam-hot air blend having a temperature of between 200 and 300 F and arelative humidity of between and 50% has been found to be desirable.Preferred conditions for other materials may differ, but thedetermination of such conditions will be readily ascertained by thoseskilled in the art.

The static bed is maintained in the conditioning atmosphere for asufficient time to effect the desired fusion. The fused bed of particlesmay then be cooled and passed through a suitable grinder or comminutorwhere the rigid fused sheet is subdivided to desired size. Physicaldifferences in the starting particle size, moisture and temperature ofthe conditioning atmosphere, bed depth and time of conditioning areamong the factors which will govern the density, degree of hardness andcolor of the fused sheet.

This invention is further described by the following specificembodiments.

EXAMPLE 1 Spray dried instant coffee having a particle size distributionof between 40 and 325 microns and a moisture content of about 3% wasspread evenly to a bed depth of 0.7 inch on a porous tray. The tray wasplaced in a dryer and hot humid air having a temperature of 260 F and aR.H. of 18% was blown down upon the bed at a velocity of about 80 feetper second. After a period of 20 minutes the tray was removed andallowed to cool. The coffee material was found as a hard fused sheetapproximately 0.5 inch in thickness and having a relatively light color.The fused sheet was ground and sieved using 7 and 40 mesh U.S. Screens.The particles passing thru the 7 mesh screen and retained on the 40 meshscreen had a bulk density of 0.2 gms/ce, were hard, light in color andresembled commercial freeze dried coffee.

EXAMPLE 2 The spray dried coffee of Example 1 was agglomerated in acontinuous manner by mechanically spreading a 0.5 inch thick bed ofcoffee on the surface of a continuous metal belt. This was accomplishedby allowing the coffee to drop onto the belt behind a darn which was set0.5 inch from the top of the belt. The belt with the 0.5 inch bed ofcoffee was passed through an openended enclosure where a steam-hot airmixture was introduced into one end of the enclosure and allowed to exitfrom the other end. The steam-hot air mixture was introduced at avelocity of about feet per second and with a temperature of 250 F and a12% RH. Additional heat was supplied by condensing steam under the belt.The coffee was conveyed through the enclosure in 2 minutes, during whichtime the static bed of coffee on the belt fused into a sheet. The sheetof fused coffee while still on the belt was then passed over a sectionwhere it was cooled by circulating tap water beneath the belt. The fusedand cooled sheet was removed from the belt and ground to desired size.

Having thus described the invention what is claimed 1. A method foragglomerating soluble coffee particles comprising the steps of:

a. forming a static bed of less than 1 inch thickness of soluble coffeeparticles having a moisture content of less than 5%,

b. contacting said static bed with an agglomerating atmosphere,consisting of humid hot air having a temperature between 200 and 300 F.and a relative humidity between 10% and 50%, for a sufficient time tomake tacky the surfaces of the coffee particles while adding not morethan 1.5% by weight moisture to the particles, whereby the particles arefused into a porous compacted sheet material,

c. cooling the fused porous sheet to produce a hard,

rigid sheet structure, and

d. grinding said rigid porous sheet into a multiplicity of agglomerates,each agglomerate containing a plurality of fused particles.

2. The method of claim 1 wherein the coffee is unground spray driedcoffee.

3. The method of claim 1 wherein the static bed is formed on acontinuous supporting member to a depth of less than 0.75 inch and thebed is passed through an agglomerating zone.

4. The method of claim 1 wherein the agglomerating atmosphere is passeddown through the static bed.

5. The method of claim 4 wherein the static bed is supported on a porousmember.

2. The method of claim 1 wherein the coffee is unground spray driedcoffee.
 3. The method of claim 1 wherein the static bed is formed on acontinuous sUpporting member to a depth of less than 0.75 inch and thebed is passed through an agglomerating zone.
 4. The method of claim 1wherein the agglomerating atmosphere is passed down through the staticbed.
 5. The method of claim 4 wherein the static bed is supported on aporous member.